1. Field of the Invention
The present invention relates to glass for a magnetic recording medium substrate that is suitable as a substrate material for magnetic recording media such as hard disks; a magnetic recording medium substrate employing the above glass and a method of manufacturing the same; a magnetic recording medium substrate blank usable for obtaining the above substrate; a magnetic recording medium equipped with the above substrate and a method of manufacturing the same; and a magnetic recording apparatus equipped with the above substrate.
2. Discussion of the Background
With the development of information-related infrastructure such as the Internet, the need for information recording media such as magnetic disks and optical disks has increased sharply. The main structural components of the magnetic memory devices of computers and the like are magnetic recording media and magnetic heads for magnetic recording and reproduction. Known magnetic recording media include flexible disks and hard disks. Of these, examples of the substrate materials employed in hard disks (magnetic disks) include aluminum substrates, glass substrates, ceramic substrates, and carbon substrates. In practical terms, depending on size and application, aluminum substrates and glass substrates are primarily employed. In the hard disk drives of laptop computers, along with higher density recording of magnetic recording media in addition to impact resistance, the requirement of increased surface smoothness of the disk substrate is intensifying. Thus, there are limits to how well aluminum substrates, with afford poor surface hardness and rigidity, can respond. Accordingly, the development of glass substrates is currently the mainstream (see, for example, Documents 1 to 10 and the following English language family members, which are expressly incorporated herein by reference in their entirety).
In recent years, with the goal of achieving even higher density recording in magnetic recording media, the use of magnetic materials of high magneto-anisotropic energy (magnetic materials of value), such as Fe—Pt and Co—Pt based materials, is being examined (see, for example, see Document 11 and the following English language family members, which are expressly incorporated herein by reference in their entirety). It is necessary to reduce the particle diameter of the magnetic particles to achieve higher density recording. However, when just the particle diameter is reduced, the deterioration of magnetic characteristics due to thermal fluctuation becomes a problem. Magnetic materials of high Ku value tend not to be affected by thermal fluctuation, and are thus expected to contribute to the achievement of greater recording density.
Document 1: Published Japanese Translation of a PCT international publication for patent application (TOKUHYO) No. Heisei 9-507206 or English language family member U.S. Pat. No. 5,958,812
Document 2: Japanese Unexamined Patent Publication (KOKAI) No. 2007-51064 or English language family member U.S. Pat. No. 5,900,296
Document 3: Japanese Unexamined Patent Publication (KOKAI) No. 2001-294441
Document 4: Japanese Unexamined Patent Publication (KOKAI) No. 2001-134925
Document 5: Japanese Unexamined Patent Publication (KOKAI) No. 2001-348246
Document 6: Japanese Unexamined Patent Publication (KOKAI) No. 2001-58843 or English language family member US2002/010066A1 and U.S. Pat. No. 6,949,485
Document 7: Japanese Unexamined Patent Publication (KOKAI) No. 2006-327935
Document 8: Japanese Unexamined Patent Publication (KOKAI) No. 2005-272212 or English language family members US 2005/215414A1 and U.S. Pat. No. 7,687,419
Document 9: Japanese Unexamined Patent Publication (KOKAI) No. 2004-43295 or English language family member US2003/220183A1, U.S. Pat. No. 7,309,671, US2008/053152A1, and U.S. Pat. No. 7,767,607
Document 10: Japanese Unexamined Patent Publication (KOKAI) No. 2005-314159 or English language family members US 2005/244656A1 and U.S. Pat. No. 7,595,273
Document 11: Japanese Unexamined Patent Publication (KOKAI) No. 2004-362746 or English language family members US 2004/229006A1 and U.S. Pat. No. 7,189,438